1. Field of the Invention
This invention relates to compatible blends of imidized acrylic polymers and polyamides and more particularly to compatible blends, of polyglutarimides and nylons, which possess desirable characteristics of each of the individual polymers.
2. Description of the Prior Art
In general, physical blending of polymers has not been a successful route for combining into a single material the desirable individual characteristics of two or more polymers. Typically, blends of polymers result in a material which combines the poorest characteristics of each polymer such that the resulting blend is not of any practical value. Thermodynamics, and particularly the entropy of mixing polymers, dictates that most polymer blends will not be miscible or compatible and will result in a material having two or more distinct phases, each containing predominantly only one of the starting polymers. Miscibility, as used herein, refers to the complete intermixing of the individual polymers in each other on a molecular level to form a solution. Compatibility, as used herein, is a more general term than miscibility but should not be confused with miscibility. Compatibility describes the ability of polymers to combine together for beneficial results. Compatible polymer blends appear macroscopically uniform, although on a molecular level the individual polymers may or may not be completely miscible in each other and may or may not form true polymer solutions.
In order to obtain combinations of polymers which exhibit the desirable characteristics of each polymer, copolymerization of the polymers or the incorporation of compatibilizers which are soluble in each of the polymers have been employed. U.S. Pat. No. 4,090,996; Mechanical Properties of Polypropylene--Low Density Polyethylene Blends, Nolley, Barlow and Paul, Polymer Engineering and Science, March 1980, Vol. 20, No. 5, p. 364; A Brief Review of Polymer Blend Technology, Paul and Barlow, Multiphase Polymers, Copper and Estes, Adv. Chemical Series 176 (1979); Block Copolymers, Allport and Janes, p. 365.
Polyglutarimides, including those disclosed in U.S. Pat. No. 4,246,374 to Kopchik, possess good thermal stability, high service temperatures (.degree.C. Vicat), high tensile strength, solvent and hydrolysis resistance, good weatherability properties, low melt flow rates, and high melt strength. Polyglutarimides are, however, brittle and exhibit poor impact resistance. The impact resistance or toughness of neat polyglutarimides may be improved by the addition of conventional impact modifiers, for example, ABS (acrylonitrile/butadiene/styrene), MBS (methylmethacrylate/butadiene/styrene), all acrylic modifiers, polycarbonates, and mixtures thereof (U.S. Pat. Nos. 4,217,424 and 4,254,232). However, it has been found that conventional polycarbonate-containing impact modifier systems for polyglutarimides are not miscible or compatible with polyglutarimides and can result in anisotropy in injection molded articles prepared therefrom. This injection molding induced anisotropy is caused by the melt flow orientation of insoluble, deformable inclusions of polycarbonate in the polyglutarimide. As a result, the impact modified polyglutarimide is tougher in the direction of flow into a mold than it is in the transverse direction. This anisotropy makes injection molded articles prepared from conventionally impact modified polyglutarimides containing polycarbonate unsuitable for certain applications requiring uniform toughness.
Despite the commercial utility of poly(carbon)amides, referred to herein as polyamides, for example in the preparation of fibers, polyamides have been found to be unsuitable for most extrusion and blow molding processes because of their high melt flow rates and poor melt stength. Accordingly, attempts have been made to modify polyamides to achieve better strength characteristics by the incorporation of modifiers. U.S. Pat. Nos. 3,668,274; 3,796,771; and 3,784,497 disclose modifications to nylon 6 and nylon 66 by incorporating acrylic core//shell polymers. These polymer additives improve the impact resistance and melt flow characteristics of the nylons but lower other important performance parameters, such as tensile strenth and modulus, and result in opaque materials. Other patents relating to the modification of nylons include U.S. Pat. No. 3,963,799 (graft reaction of polyamide and ethylene-based rubber modifier); U.S. Pat. No. 4,035,438 (mixture of polycaprolactam and polyethylene and a graft polymer of ethylene/(meth) acrylic acid copolymer and grafted polymerized units of E-caprolactam); U.S. Pat. No. 4,086,295 (incorporation of a copolymer of ethylene and a carbonate or epoxy compound); U.S. Pat. No. 4,100,223 (incorporation of polyethylene and emulsifying copolymer of aromatic vinyl compound and an alpha,beta-unsaturated mono- and/or dicarboxylic acid or anhydride having free acid groups optionally neutralized by mono- and/or polyamides, ammonia, and esters of the mono- or dicarbocylic acid); U.S. Pat. No. 4,167,505 (acrylic core//shell modifier dispersed in higher molecular weight nylon followed by blending with low molecular weight nylon); U.S. Pat. No. 4,174,358 (polyamide matrix resin and branched or straight chain polymer of specified particle size range and tensile modulus); U.S. Pat. No. 4,246,371 (polyamide with copolymer of ethylene, (meth)acrylic acid and esters thereof); U.S. Pat. No. 4,293,662 (polyamide blended with oxidized polyethylene); U.S. Pat. No. 4,321,336 (polyamide blended with either aliphatic polyolefin, olefinic copolymer of aliphatic monoolefin, (meth)acrylic acid or esters thereof, copolymers of styrene, (meth)acrylic acid and esters thereof, copolymers of aliphatic dienes and acrylonitrile and high molecualr weight organic silicon compounds); U.S. Pat. No. 4,336,406 (polyamide and graft product of polybutadiene and grafted units of t-butyl acrylate and an acrylic acid ester with 1-4 carbon atoms in the alcohol moiety); and U.S. Pat. No. 4,346,194 (polyamide blend for low temperature impact strength and ductility formed by adding elastomeric olefin copolymer or ionic copolymer of alpha-olefin and alpha,beta-unsaturated carboxylic acid and a third copolymerizable monomer such as an acrylate or methacrylate). There are, however, no reported attempts to achieve improved impact resistance and ductility for polyglutarimides by blending the polyglutarimide with polyamides, or for achieving improved melt flow, service temperature, toughness, and improved clarity for polyamides by blending polyamides with polyglutarimides.